Technology:
In Situ Bioremediation using ORC®
- A total of 750 pounds of ORC® was injected through 18 direct-push bore holes located within the source area by pushing hollow rods with removable tips to a depth of 28 ft, and then pumping ORC®-slurry through the rods as they were raised from a depth of 28 ft to 18 ft.
- An additional 150 pounds of ORC® was injected through 12 direct-push bore holes located at the property boundary.
- Groundwater samples were collected from representative monitoring wells prior to injection and then approximately monthly for five months after injection
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Cleanup Authority:
State |
Contaminants:
MTBE, BTEX
- MTBE concentrations as high as 13,000 ug/L
- BTEX concentrations as high as 25,000 ug/L |
Waste Source:
Leaks from gasoline storage tanks |
Type/Quantity of Media Treated:
Groundwater
- The direction of groundwater flow at the site is west to southwest at an average gradient of 0.0037 ft/ft and velocity of 0.067 to 0.24 ft/day
- The quality of the groundwater in the area of the site is classified as poor due to high concentrations of dissolved solids |
Purpose/Significance of Application:
Use of in situ Bioremediation using Oxygen Release Compound (ORC®) to treat MTBE in groundwater |
Regulatory Requirements/Cleanup Goals:
No information about specific treatment goals was provided |
Results:
- For the first two months following the injection of ORC®, MTBE, BTEX constituents, and TPH concentrations in well MW-14 (located in the source area) decreased and the oxidation/reduction potential increased to a positive value, indicating an increase in the oxidation conditions in the subsurface
- After the second month, concentrations of MTBE, BTEX constituents, and TPH rose to pre-injection levels and the oxidation/reduction potential decreased to a negative number
- By the fifth month (day 155), concentrations of MTBE, BTEX constituents, and TPH were above pre-injection levels
- According to the vendor, possible reasons for the increases in concentrations included: 1) actual dissolved fuel hydrocarbon concentrations may have been higher than expected, exhausting the oxygen before all hydrocarbons were metabolized; 2) the elevated salinity of the groundwater may have caused the DO to be released at a rate higher than could be used by existing site microbes; and 3) fuel hydrocarbons which remained adsorbed to the soil particles in the capillary fringe may have provided a source to reintroduce hydrocarbons in the dissolved phase. |
Cost Factors:
No cost information for this application was provided. |
Description:
The site is an active gasoline service station located on the coast of southern California, at the mouth of San Juan Creek Valley, about one-third of a mile north of the Pacific Ocean. In the early 1990's, two underground gasoline storage tanks were replaced and soil contaminated with petroleum hydrocarbons was found beneath the tank cavity and one of the gasoline dispenser islands. TPH concentrations were found in soil at levels up to 9,000 mg/kg. In groundwater, BTEX compounds were found at levels as high as 25,000 ug/L for benzene, and MTBE was found at levels as high as 13,000 ug/L. There are two dissolved-phase plumes at the site, BTEX and MTBE. In the mid-1990's, soil vapor extraction (SVE) was used at the site for approximately 13 months. While data on SVE performance was not provided, the technology did not have a long-term impact on the concentrations of dissolved-phase hydrocarbon in the saturated zone, and fuel remained adsorbed to soil within the vadose zone. ORC® was injected at the site to reduce the dissolved-phase concentrations of BTEX and MTBE and to contain the contaminant plume.
A total of 750 pounds of ORC® was injected through 18 direct-push bore holes located within the source area and sn additional 150 pounds of ORC® was injected through 12 direct-push bore holes located at the property boundary. The application of ORC® initially reduced contaminant concentrations in the groundwater for MTBE, BTEX, and TPH. However, after two months, contaminant concentrations began to rise and were above the pre-injection levels by the fifth month. Possible reasons for the increase in concentration included the presence of a continuing source of hydrocarbons and subsurface conditions that adversely affected the existing microbes at the site. |
